Know prior art discloses various on-board radar systems for detecting objects in the vicinity of a travelling host vehicle. For example, U.S. Pat. No. 5,767,803 discloses a forward-looking system that is said to be capable of distinguishing an on-coming vehicle that is in the same lane as the host vehicle from an on-coming vehicle that is not. U.S. Pat. No. 6,522,287 discloses a pre crash sensor used to activate a side air back in case of an expected impact of a vehicle. The disclosed solution comprises sensors using an aperture which is aimed laterally when the vehicle is travelling in forward direction.
The proposed solution of an actuated sensor optic has the disadvantage that this can be only done for a short time period requesting a actuation in forward direction. The mechanical parts of such an adaptive solution are expensive and arise problems for the data reliability. For optical sensors this solution will not work. The solution is tolerant versus the objects detected which mean that a security signal could be produced by an artefact, because the detected objects are not classified.
The U.S. Pat. No. 6,907,335 discloses a radar sensor based system in which a pre crash function is realized. The severity of an accident caused by an impact is determined by the type and the velocity of obstacles. According the U.S. Pat. No. 6,907,335 an obstacle is classified on the basis of pre-crash sensor signals by determining the obstacle velocity, acceleration, and acceleration change. Radar sensor signals allow the detection of objects, but for a classification several assumptions are necessary to avoid failure alarm for example when a pedestrian is detected.